I have a couple of the early 1970's Futaba square case transmitters, the ones with the built in charger and the beige vinyl coating, they were well used by pilots who flew glow engines, so the vinyl surfaces are almost black with dried castor oil grime.

I've tried Windex and Mr Mussel, to no avail, is there a solvent that will not melt the vinyl and still clean it?

Installers of UPVC windows use a fantastic solvent cleaner which I now use for cleaning all sorts of things, including old vinyl clad transmitters. This was one to come up on ebay but there are many different brands and I am sure something similar will be available in Oz......

You wont believe it, all the UPVc cleaners available are only located in the UK, maybe, plastic windows don't fair well in the Australian sun. I have some IPA I'll try and other window cleaners. The only UPVc cleaner I can find supplied in Oz is a polish for eye guards on fireman's helmets.

I've had good success with spray on whiteboard cleaner, but most recently I've been using Phil's suggested Bar Keepers Friend. I picked it up from a local Oz supplier on eBay for about $10 (from memory) delivered